1.
Being functional in PHP
David de Boer14 May 2016

2.
functional

3.
functions

4.
y = f(x)
f: X → Y

5.
functional programming
functional thinking
functional communication
not languages

6.
Why should you care?

7.
f(x)
Others
PHP
C++
C
Java

8.
– Robert C. Martin
“There is a freight train barreling
down the tracks towards us, with
multi-core emblazoned on it; and
you’d better be ready by the time
it gets here.”

9.
λ
closures
__invoke
2001 2009 2011 2012
array_map
array_filter
callable
Slim
Silex
middlewaresSymfony2

10.
2013 2014 2015 2016
PSR-7
anonymous
classes
foreach
promises
futuresStackPHP

11.
“The limits of my language
mean the limits of my world.”
– Ludwig Wittgenstein

12.
I’m David
/ddeboer
@ddeboer_nl

13.
Erlang: The Movie

14.
Erlang
Concurrent
Passing messages
Fault-tolerant

15.
Let’s begin$ brew install erlang
$ erl
Erlang/OTP 18 [erts-7.2.1] [source] [64-bit] [smp:4:4] [async-threads:
10] [hipe] [kernel-poll:false] [dtrace]
Eshell V7.2.1 (abort with ^G)
1>
on OS X
REPL

16.
➊

17.
<?php
$sum = 0;
for ($i = 1; $i <= 5; $i++) {
$sum = $sum + $i;
}
echo $sum;
// 15

18.
-module(math).
-export([sum/1]).
sum(Number) ->
Sum = 0,
Numbers = lists:seq(1, Number),
lists:foreach(
fun(N) ->
Sum = Sum + N
end,
Numbers
),
Sum.
math:sum(5).
no return
keyword
** exception error: no match
of right hand side value 1

19.
1> X = 5.
5
2> X.
5
3> X = X * 2.
** exception error: no match of right hand side value 10
4> 5 = 10.
** exception error: no match of right hand side value 10
but isn’t
looks like
assignment

20.
1> lists:sum(lists:seq(1, 5)).
15

21.
➋

22.
Imperative<?php
$sum = 0;
for ($i = 1; $i <= 5; $i++) {
$sum = $sum + $i;
}
iteration
keeps
changing

23.
-module(math2).
-export([sum2/1]).
sum2(Number) ->
List = lists:seq(1, Number),
sum2(List, 0).
sum2([], Sum) -> Sum;
sum2([H|T], Sum) -> sum2(T, H + Sum).
3> math2:sum(5).
15
empty list
separate head from tail recurse
pattern
matches
generate list

24.
Declarative 1<?php
// Declare a function!
function sum($x)
{
if ($x == 0) {
return $x;
}
return $x + sum($x - 1);
}
sum(5);
// still 15
$x never
changes
recursion

25.
Declarative 2<?php
function sum2($number)
{
array_sum(range(1, $number));
}
echo sum2(5);
// yuuuup, 15 again
functionfunction
composition

26.
Some history

27.
Church Von Neumann
declarative imperative

28.
A lot of our code is about the
hardware it runs on
But programmers should worry
about the conceptual problem domain

29.
Recursion-module(math).
-export([fac/1]).
fac(0) -> 1;
fac(N) -> N * fac(N - 1).
1> math:fac(9).
362880

30.
Recursion fail-module(math).
-export([fac/1]).
fac(0) -> 1;
fac(N) -> N * fac(N - 1).
%%fac(9) = 9 * fac(9 - 1)
%% = 9 * 8 * fac(8 - 1)
%% = 9 * 8 * 7 * fac(7 - 1)
%% = 9 * 8 * 7 * 6 * fac(6 - 1)
%% = 9 * 8 * 7 * 6 * 5 * fac(5 -1)
%% = 9 * 8 * 7 * 6 * 5 * 4 * fac(4 - 1)
%% = 9 * 8 * 7 * 6 * 5 * 4 * 3 * fac(3 - 1)
%% = 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * fac(2 - 1)
%% = 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1 * fac(1 - 1)
%% = 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1 * 1
%% = 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1
%% = 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2
%% = 9 * 8 * 7 * 6 * 5 * 4 * 6
%% = 9 * 8 * 7 * 6 * 5 * 24
%% = 9 * 8 * 7 * 6 * 120
%% = 9 * 8 * 7 * 720
%% = 9 * 8 * 5040
%% = 9 * 40320
%% = 362880
10 terms in
memory

31.
Tail recursion-module(math).
-export([tail_fac/1]).
tail_fac(N) -> tail_fac(N, 1).
tail_fac(0, Acc) -> Acc;
tail_fac(N, Acc) -> tail_fac(N - 1, N * Acc).
tail_fac(9) = tail_fac(9, 1).
tail_fac(9, 1) = tail_fac(9 - 1, 9 * 1).
tail_fac(8, 9) = tail_fac(8 - 1, 8 * 9).
tail_fac(7, 72) = tail_fac(7 - 1, 7 * 72).
tail_fac(6, 504) = tail_fac(6 - 1, 6 * 504).
tail_fac(5, 3024) = tail_fac(5 - 1, 5 * 3024).
…
tail_fac(0, 362880) = 362880
do calculation
before recursing

32.
➌

33.
$object->setFoo(5);
$value = $object->getFoo();
no
return
value
no input
value

34.
$object->setFoo(5);
$value = $object->getFoo();
$object->setFoo('Change of state!');
$value = $object->getFoo();
no
return
value
no input
value
same argument,
different return value

35.
No side-effects
A pure function
does not rely on data outside itself
does not change data outside itself

36.
Object orientation
Solve problems with objects
Objects have internal state
Modify state through methods

37.
With side-effectsclass Todo
{
public $status = 'todo';
}
function finish(Todo $task)
{
$task->status = 'done';
}
$uhoh = new Todo();
$uhoh2 = $uhoh;
finish($uhoh);
echo $uhoh->status; // done
echo $uhoh2->status; // done???

38.
No side-effectsclass Todo
{
public $status = 'todo';
}
function finish(Todo $task)
{
$copy = clone $task;
$copy->status = 'done';
return $copy;
}
$uhoh = new Todo();
$finished = finish($uhoh);
echo $finished->status; // done
echo $uhoh->status; // todo
cloning is
cheap

39.
Some state
must change

40.
Read/write database
Get user input
Current date and time
Random values (security)

41.
Immutable objects
PSR-7 HTTP messages
Domain value objects
DateTimeImmutable
Service objects

42.
➍

43.
Higher-order functions
Functions are values
so they can be arguments
and return values

44.
$names = ['Billy', 'Bob', 'Thornton'];
$anonymise = anonymise('sha256');
var_dump(array_map($anonymise, $names));
// array(3) {
// [0]=>
// string(64) "85eea4a0285dcb11cceb68f39df10d1aa132567dec49b980345142f09f4cb05e"
// [1]=>
// string(64) "cd9fb1e148ccd8442e5aa74904cc73bf6fb54d1d54d333bd596aa9bb4bb4e961"
// [2]=>
// string(64) "d7034215823c40c12ec0c7aaff96db94a0e3d9b176f68296eb9d4ca7195c958e"
// }
using PHP built-ins

45.
$names = ['Billy', 'Bob', 'Thornton'];
$anonymise = anonymise('sha256');
var_dump(array_map($anonymise, $names));
// array(3) {
// [0]=>
// string(64) "85eea4a0285dcb11cceb68f39df10d1aa132567dec49b980345142f09f4cb05e"
// [1]=>
// string(64) "cd9fb1e148ccd8442e5aa74904cc73bf6fb54d1d54d333bd596aa9bb4bb4e961"
// [2]=>
// string(64) "d7034215823c40c12ec0c7aaff96db94a0e3d9b176f68296eb9d4ca7195c958e"
// }
function anonymise($algorithm)
{
return function ($value) use ($algorithm) {
return hash($algorithm, $value);
};
}
higher-order function
closure
using PHP built-ins
function as value
function as argument

46.
Middleware<?php
use PsrHttpMessageRequestInterface;
function add_header($header, $value)
{
return function (callable $handler) use ($header, $value) {
return function (
RequestInterface $request,
array $options
) use ($handler, $header, $value) {
$request = $request->withHeader($header, $value);
return $handler($request, $options);
};
};
}
$myStack = (new MiddlewareStack())
->push(add_header('Silly-Header', 'and its value'));
call next
in stack
immutable
higher-order function

47.
Middleware<?php
use PsrHttpMessageServerRequestInterface as Request;
use PsrHttpMessageResponseInterface as Response;
$app = new SlimApp();
$app->add(function (Request $request, Response $response, callable $next) {
$response->getBody()->write('Hey there, ');
$response = $next($request, $response);
$response->getBody()->write('up?');
return $response;
});
$app->get('/', function ($request, $response, $args) {
$response->getBody()->write('what’s');
return $response;
});
$app->run();
// Hey there, what’s up?
stream is not
immutable
before
after

48.
➎

49.
Composition over
inheritance

50.
Service objects<?php
namespace SymfonyComponentSecurityCore;
interface SecurityContextInterface
{
public function getToken();
public function isGranted($attributes, $object = null);
}

51.
Service objects<?php
namespace SymfonyComponentSecurityCoreAuthenticationTokenStorage;
interface TokenStorageInterface
{
public function getToken();
}
namespace SymfonyComponentSecurityCoreAuthorization;
interface AuthorizationCheckerInterface
{
public function isGranted($attributes, $object = null);
}
single function

52.
Single responsibility
taken to its
logical conclusion

53.
You may not need
all those patterns

54.
Take-aways
Reduce and isolate side-effects
Create immutable value objects
Be declarative

55.
More?

56.
Thanks!
https://joind.in/talk/bc26a
@ddeboer_nl